1. Field of the Invention
The present invention relates to a photoelectric conversion element and an imaging element in which a photoelectric conversion layer that generates a charge in response to received light is configured using an organic compound and which convert a visible light image into an electrical signal and particularly relates to a photoelectric conversion element an imaging element which have a small dark current and are capable of obtaining a high-resolution image.
2. Description of the Related Art
As an image sensor used for a digital still camera, a digital video camera, a camera for a mobile phone, or a camera for an endoscope, a solid-state imaging element such as a charge coupled device (CCD) sensor or a complementary metal oxide semiconductor (CMOS) sensor which arranges pixels including photodiodes on a semiconductor substrate such as a silicon chip and in which a signal charge corresponding to a photoelectron generated by a photodiode of each pixel is acquired by a CCD type or CMOS type read circuit has been widely known. Meanwhile, a photoelectric conversion element using an organic compound has been developed. In order to improve imaging characteristics, a dark current thereof is required to be small and, accordingly, various elements having a reduced dark current have been suggested (JP2011-228623A and JP2011-199263A).
JP2011-228623A discloses a photoelectric conversion element which includes a pair of electrodes and a photoelectric conversion layer interposed between the pair of electrodes. The photoelectric conversion layer of the photoelectric conversion element in JP2011-228623A is a bulk hetero-layer in which fullerenes or a fullerene derivative and a P-type organic semiconductor material are mixed with each other, and the ionization potential of the photoelectric conversion layer is in a range of 5.2 eV to 5.6 eV. At least one electron blocking layer is provided between at least one electrode from a pair of electrodes and the photoelectric conversion layer, and the ionization potential of the electron blocking layer adjacent to the photoelectric conversion layer is greater than the ionization potential of the photoelectric conversion layer.
JP2011-199263A discloses an organic photoelectric conversion element which includes a photoelectric conversion layer including a first electrode, a second electrode facing the first electrode, and an organic material provided between the first electrode and the second electrode. In the organic photoelectric conversion element of JP2011-228623A, the number of electron spins of the photoelectric conversion layer is 1.0×1015/cm3 or less.